The proposed work will be along three principal lines: 1) To devise a fluorescence histochemical method for sensitive studies of catecholamine neurons based on glyoxylic acid (GA) as fluorescence forming reagent. The kinetics and the exact mechanisms of the reaction between GA and catecholamines will be studied, and procedures for microspectrofluorometric identification of the GA-catecholamine reaction products will be devised. In parallel we will make efforts to modify the present technique for optimal demonstration of indolamines. In our opinion it should be possible in this way to develop a technique for this class of amines that is as useful as the present one is for catecholamines. 2) To initiate studies with this method on central catecholamine neurons. A major part of our efforts will be directed towards studies of the organization of the dopamine and noradrenaline neuron systems as revealed by the GA method. This will then also include the description of several new features and principles of their organization. 3) To investigate the usefulness of a recently introduced class of neurotoxic hydroxylated tryptamines for experimental and neuroanatomical studies on central indolamine neurons. This work will proceed along two lines: a) a search for derivatives of 5,6-DHT with biologically useful neurotoxic properties, and b) to study the usefulness of 5,6-DHT and 5,7-DHT for neuroanatomical studies on central indolamine neurons.